Much of the world, including much of the highly industrialized parts of the world, has a chronic shortage of fresh water for any and all uses. This shortage has led to increasing employment of seawater or brackish water in the cooling of chemical process equipment and power plants. Consequently, there has been an increased need for materials of construction that are resistant to seawater and to chemical process streams that may be cooled with seawater. Of course, there is also great advantage in metal alloys resistant to seawater for numerous ship, platform and dock construction applications.
Remarkable alloys have been developed for resistance to salt water plus some limited ranges of chemical substances. Some of these, such as Hastelloy B, Hastelloy C, Hastelloy G, Inconel 625, Illium B, and Allcorr have excellent resistance to chloride and certain other substances, but consist almost entirely of strategic elements and are hence extremely expensive and, therefore, limited in use.
Of more recent invention have been less-expensive, highly-modified stainless steels for seawater resistance. These include the ferritic type, available only in wrought forms, and austenitic types such as Al-6X, 254SMO, 904L, VEWA963, NSCD and SANICRO 28. While some of these have rather low strategic element content, each has one or more disadvantages. Seawater resistance may be high but not complete, such that there remain instances of failure under fouling, during shutdown periods, or otherwise. In some instances, fabricability and weldability are possible but somewhat limited and costly. In other instances, resistance to seawater is excellent, but resistance ot other agents, such as various chemical process streams, is somewhat limited. Some variations may be available only as cast shapes.
Hence, there remains a need for alloys of relatively low strategic element content but which are completely resistant to seawater and a wide range of chemical substances, and yet are truly very highly fabricable.
Japanese Pat. No. 9182-937A describes an electricity application roll for electric plating. The roll is constructed of an alloy consisting of less than 0.05% by weight carbon, less than 1.00% by weight silicon, less than 2.00% by weight manganese, 18.0% to 25.0% by weight chromium, 5.00% to 8.00% by weight molybdedum, 18.0% to 25.0% by weight iron, 1.06% to 5.00% by weight copper, niobium and/or tantalum in a proportion of 1.75% to 2.50% by weight, and at least one from among aluminum in a proportion of less than 0.5% by weight, titanium in a proportion below 1.00% by weight, and cobalt in a proportion below 5.00% by weight. The balance of the alloy is nickel. The alloy is said to have sufficient corrosion resistance even when the plating liquid is at PH 0.6 to 1.6. The included proportions of niobium plus tantalum provides for stabilization of carbon in the austenite phase and are said to provide intergranular corrosion resistance. The iron inclusion is described as providing excellent hot workability as well as weldability.
Mott U.S. Pat. No. 3,044,871 describes a hardenable corrosion-resistant stainless steel adapted to handle corrosives where an erosion or abrasion condition exists. The alloys broadly contain up to 0.07% by weight carbon, 15% to 32.5% by weight chromium, 25% to 35% by weight nickel, 0.2% to 7% by weight silicon, 0.2% to 4% by weight manganese, 1% to 5% by weight copper and 2% to 20% by weight molybdenum. Consistent with the objective of achieving hardness and erosion resistance, many of the alloys contain significant proportions of silicon in the range of approximately 2.0% to 5.0%.
Baumel U.S. Pat. No. 3,726,668 describes a welding filler material containing 0.001% to 0.2% by weight carbon, 0.1% to 5.0% by weight silicon, 0.25% to 10.0% by weight manganese, 15.0% to 25.0% by weight chromium, 3.5% to 6.0% by weight molybdenum, 8.0% to 30.0% by weight nickel, 0.01% to 3.0% by weight copper, 0.1% to 0.35% by weight nitrogen, related to the total weight of the metallic constituents and carbon, the balance essentially iron and inevitable impurities. The filler material is said to be useful in providing fully austenitic surface weld layers or welded joints which are insusceptible to hot cracking on predominantly austenic base materials, particularly chromium-nickel steels.
Japanese Pat. No. 7171-651 describes austenitic stainless steel having good weld zone corrosion resistance and consisting of less than 0.04% by weight carbon, less than 1.5% by weight silicon, less than 2.0% by weight manganese, 18.0% to 25.0% by weight chromium, 20.0% to 30.0% by weight nickel, 4.0% to 8.0% by weight molybdenum, 0.01% to 0.3% by weight nitrogen, aluminum in a proportion of less than 0.02% by weight, lanthanum plus cerium in a proportion of 0.01% to 0.06% by weight, additional boron in a proportion of less than 0.01% by weight, or copper in a range of 0.3% to 3.0% by weight with boron less than 0.1%, and the balance essentially iron and impurities. The steel is said to be always in the austenitic state irrespective of any heat treatment and to have good corrosion resistance to sea water and in the weld zone.
A need has remained in the art for alloys of relatively low strategic metal content which can be used in corrosive chemical process stream service, and in particularly in applications requiring resistance to chloride stress corrosion.